The system layer describes the functional subsystems. From the perspective of system design, each subsystem has its own specifications, including resource requirements (i.e., computation and storage), connectivity requirements, specific capacity and other properties of relevance for the DIMA architecture design such as their Design Assurance Level (DAL) or specific hardware dependencies. As shown in Figure 2, DIMA system is broken down into a hierarchical tree of subsystems, with the root node representing the entire system^[1]. Typical subsystems in the aircraft can be Bleed-Air System (BAS), Overheat Detection System (OHDS), Pneumatic System (PS) and Ventilation Control System (VCS)^[2]. The purpose of this layer is to capture the system logic, tasks and connections, as well as peripherals and interfaces for functional subsystems.

Each of the subsystems in the system layer is composed of functions from an architectural point of view. Such an abstraction in form of functions is beneficial to reduce the complexity of the system. Typical functions of the aircraft include but are not limited to: aileron control, multi-function spoilers control, ground spoilers control, rudder control and brake function. For example, an aileron controller function is in charge of monitoring and actuating flight control surfaces. It may consist of a sensor acquisition module, a monitor module, and an actuator controller module. These modules are enabled by a set of hardware components in the hardware layer, including CPMs, RDCs and sensors.

The hardware layer contains hardware devices, their configurations, and network topology, which support the functions in the system layer. The main categories of DIMA devices are sensors, actuators, cables, switches, Core Processing Modules (CPMs), Remote Data Concentrators (RDCs), and Input/Output (I/O). The purpose of these devices is to provide the necessary resources (computing power, memory, data storage, etc.) to the system. Each device is characterized by its type (Central Processing Units (CPUs), network hardware, or peripherals), vendor, weight, volume, power, input ports, output ports and supported signal types. Such characteristics are important in designing the quality measures and constraints in the optimization problem. The details of the DIMA devices are as follows.

The installation layer describes hardware allocation to the anatomy of underlying aircraft. It is powered by mount locations and power network.

Hardware devices can be installed at different mount locations of the aircraft, such as cockpit, avionics bay, middle, tail, and so forth. The installation location is characterized by its coordinates, volume, cooling capacity, power supply, number of slots and mass. The location characteristics should be considered for the optimization on installation of devices. While placement of some components are fixed (e.g. sensors and actuators), CPMs placement and cable routing are needed to determine for the optimization subject to constraints, such as physical and safety requirements.

The power network enables the mount locations to be connected with tunnels, which provides power for the devices installed at the location. Such a network is different from the one in the hardware layer that represents communication network among the devices.

These three layers are interconnected via hardware and software mapping in the DIMA system. Particularly, the hardware and software mapping can include the followings:

(1) Device assignment: it maps devices to locations in the aircraft. The assignment should consider connectivity and physical constraints.